The present invention relates to electronic still photography, and more particularly, to a digital still camera (DSC) with an improved method of determining and indicating to a user the number of pictures that can still be taken with the camera and recorded in its internal or removable memory.
DSCs are rapidly gaining in popularity with consumers as an alternative to conventional still cameras that use silver halide film. The number of pixels in charge coupled device (CCD) image sensors has increased to the point where picture detail and clarity are acceptable to consumers. The digital images can be selected and enhanced before printing with home photo album software, eliminating the cost and inconvenience of purchasing and developing traditional camera film. Advancements in ink jet and laser printer technology, inks and paper allow color prints to be generated from digital images that rival the quality of silver halide color prints. Digital images taken with a digital still camera can be cut and pasted into various word processing and other publishing applications used on personal computers (PCs). In addition, the digital images can be used in web pages and can be transmitted over the Internet. From an environmental standpoint, electronic still photography is attractive because it reduces the need for silver halide film manufacture as well as the handling and disposal of chemical developer solutions.
Film cameras typically indicate the remaining picture count to the user, i.e. they show a number on the camera housing that tells the user how many additional pictures can still be taken before the film has been used up. The remaining picture count is typically noted either before an outing with photographic opportunities, or during the outing. A typical film camera will indicate a numeral on a mechanical wheel visible through a window, or on an LCD display, representing the number of exposures left on the film, normally starting at twenty-four or thirty-six, depending on the size of the roll of film loaded in the camera. Some film cameras indicate the number of pictures taken and the user then easily determines, by subtraction, how many exposures remain on the roll of film. Clearly, with film cameras, each picture or image taken utilizes the same amount of film regardless of the camera's settings and regardless of the subject matter photographed.
Digital still cameras typically store pictures on a removable storage media such as a floppy disk, flash memory card or CD-R. The pictures are stored in either type of memory as image files which are usually recorded in a standard such as JPEG format. Various data compression techniques are utilized as is well known in the art to maximize the number of image files that can be stored on a given removable storage media. Each image file can utilize different amounts of storage space, in contrast to film images which take up the same uniform length and width of film on a roll. There are several principal factors which determine the image file size. Different photographic subjects will produce different sizes of JPEG compressed image files depending upon the level of detail in a subject. For example, all other factors being constant, a close up electronic still photograph of a bouquet of flowers would generally produce a larger image file size than a photograph of a landscape at a distance including considerable blue sky. Different selected levels of data compression will of course affect the size of the image file. Different selected picture resolutions will also result in different image file sizes for an image of the same object or scene. The picture resolution is the pixel matrix count recorded in the image file. Many digital still cameras allow the user to select standard or fine picture resolution. These are pre-set in the digital still camera and may be, for example, 1600×1200 (reflecting the layout of the CCD) and 640×480 (sub-sampled). The user must' decide between better detail in the color print image produced with the fine picture resolution versus the greater amount of memory that will be utilized not only to store the picture on the removable media but to store the picture in application software and the increased time to send the image via e-mail. In simple terms, the trade off is picture quality versus the number of pictures that can be stored in memory.
Just as with film cameras, digital still cameras have been provided with remaining picture count indication. The number of pictures that can be taken in a digital still camera depends upon the size of the available memory, either the fixed internal memory or the removable memory and the resulting size of the image files. As previously discussed, the size of the image files varies greatly, depending upon the subject, the level of data compression and the picture resolution. It is impossible to predict the subject of a picture in any remaining picture count algorithm. If such an algorithm were to base a calculation of the remaining picture count based on a predetermined estimated maximum image file size, then there would often still be available memory left when the remaining picture count went to zero. A digital still camera with this remaining picture count determination scheme would be far less competitive in the marketplace because users would think it could not store as many pictures. If such an algorithm were to base a calculation of the remaining picture count based on a predetermined estimated minimum image file size then the user might be disappointed when the camera could not take a picture even though the remaining picture count was greater than zero. If such an algorithm were to base a calculation of the remaining picture count based on a predetermined estimated average image file size then the user might suffer either or both of the aforementioned undesirable outcomes.
U.S. Pat. No. 5,027,214 of Fujimori assigned to Olmpus Optical Company, Ltd. discloses an electronic still camera in which a data compression means applies a variable length data compression to the digital signal from an A/D conversion means connected to an image pickup means and each “one-frame compressed image data” is assigned a space on the recording medium and calculating and indicating means are used to indicate the recordable number of images. The calculating means calculates an estimated count which can be recorded “in accordance with quantitative data per frame associated with the plurality of one-frame compressed image data recorded in the recording medium by said recording means and quantitative data associated with the recording capacity of the recording medium.” The calculating means of the '214 Fujimori patent can calculate an estimated count of recordable electronic still images that can be recorded in the recording medium by dividing a remaining recording capacity of the recording medium by at least one maximum, minimum and average capacities per frame of the image data.
U.S. Pat. No. 4,746,993 of Tada assigned to Sony Corporation discloses an electronic still camera which stores images in tracks on a magnetic disk and has an indicator for displaying “data concerning the use and availability of space on the record medium.” The detailed description refers to the availability of tracks since it relies on a magnetic disk and indicates that one picture can be stored per fixed number of tracks. Image resolution can be selected but it does not appear that variable-length data compression is utilized or any means for calculating the number of pictures that can still be stored based on the maximum, minimum or average size of the image files of the pictures already taken. An arithmetic circuit derives the number of occupied and available tracks which are then displayed, which number of tracks equates to the number of pictures stored and that can be stored. The '993 Tada patent indicates that the number of “shots” that can be taken can be displayed.
U.S. Pat. No. 5,034,804 of Sasaki et al. assigned to Toshiba discloses a digital still camera with variable-length encoding data compression in which the available space in the memory card is determined. If the available memory space is inadequate to store a picture, the image data is stored in a buffer memory and the next photographic operation is inhibited until a new memory card is inserted.
The techniques that have heretofore been utilized in digital still cameras to calculate the remaining picture count have been unduly complex. This adds to the processing load of the camera's microprocessor. In addition, errors in the remaining picture count can still occur under certain circumstances with these prior art approaches. Furthermore, these prior art approaches have not been designed to optimally accommodate various combinations of user selected picture resolution and user selected data compression level.